Combustion chamber for a gas turbine and burner arrangement

ABSTRACT

A combustion chamber ( 10, 20 ) for a gas turbine ( 1 ) with at least two combustion zones ( 23, 24 ) and at least one burner arrangement ( 11, 28 ) for the combustion of a fuel/air mixture in the combustion zones ( 23, 24 ). The burner arrangement ( 11, 28 ) has at least one premixing passage ( 29 ) that opens into the combustion zones ( 23, 24 ) to provide a fuel/air mixture, and an air supply ( 32 ) and at least one fuel supply ( 33 ) encompassed in the burner arrangement ( 11, 28 ) and open into the premixing passage ( 29 ). The combustion chamber permits a particularly effective damping of combustion chamber pressure fluctuations. To this end, the air supply ( 32 ) is designed in a stepped manner such that the outlet openings ( 34, 34   a,    34   b,    34   c ) of the stepped air supply that open into the premixing passage can be assigned different delay times (τ 1 , τ 2 , τ 3 ), which damps the fluctuations.

The invention relates to a combustion chamber for a gas turbine havingat least one combustion zone and at least one burner arrangement for thecombustion of a fuel/air mixture, wherein the burner arrangementcomprises at least one premixing passage which opens into the combustionzone and which serves for the provision of a fuel/air mixture, and anair supply encompassed by the burner arrangement and at least one fuelsupply open into the premixing passage.

The invention also relates to a gas turbine having a combustion chamberof said type and to a burner arrangement.

Known gas turbines comprise a compressor and a turbine in addition to acombustion chamber as mentioned in the introduction. The compressorcompresses the air supplied to the gas turbine, wherein a part of saidair serves for the combustion of fuel in the combustion chamber and apart is used for cooling the gas turbine and/or the combustion gases.The hot gases provided in the combustion chamber as a result of thecombustion process are introduced from the combustion chamber into theturbine, wherein said gases expand and cool therein and, performingwork, set turbine blades in rotation in the process. By means of saidrotational energy, the gas turbine drives a work machine. The workmachine may for example be a generator.

The fuel/air mixture provided by the at least one burner arrangement ispremixed in the at least one premixing passage for then being ignitedafter flowing into the combustion zone. The premixing of the fuel withthe air reduces the pollutant emissions generated during the combustionin relation to the hitherto conventional direct injection of the fuelinto the combustion zone. A disadvantage of the premixing of the fuel ishowever that said arrangement is significantly more susceptible to theoccurrence of combustion chamber pressure fluctuations. If pressurefluctuations occur in the combustion zone, concentration fluctuations inthe fuel/air mixture in the premixing passage also arise, which lead toheat release fluctuations during the combustion. These thermoacousticinstabilities in turn intensify the combustion chamber pressurefluctuations, wherein, in the arrangement, there are predominantfrequencies for these escalating combustion chamber pressurefluctuations. The concentration fluctuations in the fuel/air mixture,that is to say variations in the fuel/air mixture ratio over time, mayalso be referred to as air number fluctuations. The air numberfluctuations result from varying acoustic resistances of the air supplyand fuel supply. For damping the combustion chamber pressurefluctuations, known gas turbines have resonators arranged in thehousing. Since the resonators directly adjoin the combustion zone andfurthermore interrupt a heat shield arrangement in the housing and musttherefore be cooled, such a design of the combustion chamber iscumbersome. An alternative design of a known combustion chamberprovides, for the suppression of such combustion chamber pressurefluctuations, that the fuel nozzles that open into the premixing passageare arranged so as to be distributed in the axial direction along thepremixing passage, such that mixing zones with different delay times areformed in the premixing passage. Said stepped design of the fuel supplymakes it possible for the concentration fluctuations, caused by thecombustion chamber pressure fluctuation, in the fuel injected throughthe fuel supply to be smoothed. The fuel nozzles may also be referred toas outlet openings of the fuel supply.

It is an object of the invention to specify a combustion chamber of thetype mentioned in the introduction, a gas turbine having a combustionchamber of said type, and also a burner arrangement encompassed by acombustion chamber of said type, which permits particularly effectivedamping of combustion chamber pressure fluctuations.

The object is achieved according to the invention, in the case of acombustion chamber of the type mentioned in the introduction, in thatthe air supply is of stepped form such that outlet openings, which openinto the premixing passage, of the stepped air supply can be assigneddifferent delay times.

By means of the known fuel supply with fuel nozzles arranged so as to bedistributed in the axial direction along the premixing passage, it isindeed possible to compensate for fluctuations, caused by combustionchamber pressure fluctuations, in the fuel flow rate admixed to the airstream along the premixing passage. However, owing to the differentacoustic resistances of the air and of the fuel, said known steppedconfiguration is not suitable for injecting the fuel into the air streamin such a way that a constant ratio of fuel and air and a constant fuelflow rate per unit of time exits the premixing passage and enters thecombustion zone. Therefore, according to the invention, for thesuppression of combustion chamber pressure fluctuations and thus also ofheat release fluctuations, it is proposed that the air supply that opensinto the premixing passage be of stepped form, and thus the densityfluctuations, caused by combustion chamber pressure fluctuations, in theair stream passing through the premixing passage be smoothed. Owing tothe high compressibility of air in relation to, for example, a liquidfuel, and the relatively low pressure in the air supply line in relationto the pressure in the fuel supply line, this is particularly effectivefor the suppression of combustion chamber pressure fluctuations.

According to the invention, the stepped air supply comprises outletopenings that open into the premixing passage, which outlet openings canbe assigned different delay times. The stepped air supply mayfurthermore comprise further outlet openings which may be assignedredundant delay times. The delay time may also be referred to as aconvective time delay. Said time delay is defined as the time requiredfor a fluid element entering the premixing passage to pass to thecombustion zone. The outlet openings may also be referred to as exitopenings.

The burner arrangement may for example comprise a pilot burner with apremixing passage with pilot burner lance arranged centrally therein,wherein the pilot burner lance is connected to a fuel supply andcomprises fuel nozzles. An air supply opens into the premixing passageof the pilot burner. Around the pilot burner there may be arranged amultiplicity of main mixers encompassed by the burner arrangement. Eachof the main mixers may have a premixing passage encompassed by acylindrical housing, into which premixing passage an air supply opens,and axially in which premixing passage there is arranged a lance whichis connected to a fuel supply and which has fuel nozzles. The lance mayfor example be supported on the housing via swirl vanes. According tothe invention, in the case of the burner arrangement specified by way ofexample, at least one of the premixing passages comprises a stepped airsupply. It is for example possible for the air supply of each of themain mixers to be of stepped form by virtue of the swirl vanes formingair outlet openings which open into the premixing passage and which canbe assigned different delay times. Said delay times may preferably beselected such that, at least in the frequency range of a predominantcombustion chamber pressure fluctuation, density fluctuations caused bythe latter in the supplied air cancel one another out, or attenuate oneanother, owing to the different delay times of the air outlet openings.

One advantageous refinement of the invention may provide that, inaddition to the air supply of stepped form, a fuel supply which opensinto the premixing passage and which can be charged with gaseous fuel islikewise of stepped form.

Since the gaseous fuel likewise exhibits high compressibility inrelation to air, the additional stepped configuration of the fuel supplythat can be charged with gaseous fuel makes it possible forfluctuations, caused by combustion chamber pressure fluctuations, inconcentration and density of the fuel/air mixture flowing out of thepremixing passage into the combustion zone to be dampened with evengreater effectiveness. If the premixing passage comprises more than onefuel supply that can be charged with gaseous fuel, it is possible forone or more of said fuel supplies that can be charged with gaseous fuelto be of stepped form.

It may advantageously also be provided that the outlet openings of thestepped supply can be assigned delay times, wherein, for a minimum delaytime τ_(min) and a maximum delay time τ_(max) with regard to acombustion chamber pressure fluctuation, of frequency f, which is to besuppressed, the following applies: τ_(max)−τ_(min)>1/f.

By means of said condition, it is ensured that, at least in thefrequency range of the combustion chamber pressure fluctuation to besuppressed, density fluctuations, caused by the latter, in the fluidsupplied through the stepped supply are attenuated in an effectivemanner. The stepped supply is the stepped air supply. If yet furthersupplies that open into the premixing passage are of stepped form, thecondition may also apply to said supplies. The minimum and maximum delaytimes specified in the condition relate respectively to the shortest andthe longest of the delay times assigned to the outlet openings of asupply.

It may also be considered advantageous for the outlet openings, whichopen into the premixing passage, of the stepped supply to be arrangedsuch that density fluctuations, caused by at least one predominantcombustion chamber pressure fluctuation of frequency f′, in the fluidsupplied through the outlet openings are superposed on one another inthe premixing passage owing to the different delay times assigned to theoutlet openings, in such a way that said density fluctuationssubstantially cancel one another out.

In one advantageous refinement of the invention, it may be provided thatthe burner arrangement is arranged in the region of a second axialstage, with at least one premixing passage that opens into thecombustion zone, wherein the combustion zone follows downstream of afirst combustion zone with a first burner arrangement.

By means of a second axial stage, the heat release can be distributedfurther over the entire available combustion chamber, such that thesusceptibility of the combustion system to thermoacoustic instabilitiesis further reduced. Furthermore, a stepped air supply to at least onepremixing passage of the burner arrangement of the second axial stagecan be realized particularly easily in terms of apparatus.

A preferred refinement of the invention may provide that the burnerarrangement comprises a fuel distributor ring arranged around theoutside of a combustion chamber housing and comprises multiple premixingpassages, wherein the premixing passages open at one end thereof intothe combustion zone in the combustion chamber housing and correspond toat least one fuel supply that branches off from the fuel distributorring, wherein outlet openings of a stepped air supply are arranged so asto be distributed at least along one of the premixing passages.

Said stepped air supply to at least one premixing passage of the burnerarrangement of the second axial stage can be realized particularlyeasily in terms of apparatus. The premixing passages may for example beof hose-like form, wherein, for the present invention, it is verygenerally the case that the position of the air outlet openings alongthe premixing passages, or the delay times corresponding thereto, may beadaptable to the frequency of the combustion chamber pressurefluctuations to be suppressed. For example, the hose-like premixingpassage may be composed of elastic material, wherein the length of saidpremixing passage—and thus also the delay times corresponding to theoutlet openings—can be adapted to a frequency to be suppressed.

It is a further object of the invention to specify a gas turbine havingat least one combustion chamber as mentioned in the introduction, whichpermits particularly effective damping of combustion chamber pressurefluctuations.

For this purpose, the gas turbine has at least one combustion chamberwhich is designed as claimed in one of claims 1 to 4.

It is a further object of the invention to specify a burner arrangementwhich is encompassed by the combustion chamber mentioned in theintroduction and which permits particularly effective damping ofcombustion chamber pressure fluctuations.

For this purpose, the burner arrangement is a constituent part of thecombustion chamber as claimed in one of claims 1 to 4.

Further expedient refinements and advantages of the invention aredescribed in the description of exemplary embodiments of the inventionwith reference to the figure of the drawing, wherein the same referencesigns are used for equivalent components.

In the drawing:

FIG. 1 shows a schematic sectional view of a gas turbine according tothe prior art,

FIG. 2 shows, in a schematic sectional view, a detail of a combustionchamber with a second axial stage according to an exemplary embodimentof the invention, and

FIG. 3 shows, in a schematic sectional view, a detail view of theexemplary embodiment illustrated in FIG. 2 in the region of the steppedair supply.

FIG. 1 shows a schematic sectional view of a gas turbine 1 according tothe prior art. The gas turbine 1 has, in the interior, a rotor 3 whichis mounted so as to be rotatable about an axis of rotation 2 and whichhas a shaft 4 also referred to as turbine rotor. Arranged in successionalong the rotor 3 are an intake housing 6, a compressor 8, a combustionsystem 9, a turbine 14 and an exhaust-gas housing 15, the combustionsystem having a number of combustion chambers 10 which each comprise aburner arrangement 11 and a combustion chamber housing 12.

The combustion system 9 communicates with a hot-gas duct, which is forexample of annular form. There, multiple turbine stages positioned inseries form the turbine 14. Each turbine stage is formed from vanerings. In the hot duct, as viewed in the flow direction of a workingmedium, a row formed from guide vanes 17 is followed by a row formedfrom rotor vanes 18. The guide vanes 17 are in this case fastened to aninner housing of a stator 19, whereas the rotor vanes 18 of a row arefor example attached by means of a turbine disk to the rotor 3. Agenerator (not illustrated), for example, is coupled to the rotor 3.

During the operation of the gas turbine, air is drawn in through theintake housing 6, and compressed, by the compressor 8. The compressedair provided at the turbine-side end of the compressor 8 is conducted tothe combustion system 9 and mixed there with a fuel in the region of theburner arrangement 11.

The mixture is then burned with the aid of the burner arrangement 11,such that a working gas stream is formed in the combustion system 9.From there, the working gas stream flows along the hot-gas duct past theguide vanes 17 and the rotor vanes 18. At the rotor vanes 18, theworking gas stream expands with a transmission of impetus, such that therotor vanes 18 drive the rotor 3, and the latter drives the generator(not illustrated) coupled thereto.

FIG. 2 shows a detail of a combustion chamber 20 of a gas turbineaccording to an exemplary embodiment of the invention. The combustionchamber 20 has a combustion chamber housing 21 which is formedrotationally symmetrically about an axis 22. In the combustion chamberhousing 21 there is situated a first combustion zone 23 and a secondcombustion zone 24, wherein the second combustion zone 24 followsdownstream of the first combustion zone 23 in relation to a main flowdirection 26. The combustion chamber 20 comprises a first burnerarrangement (not illustrated) and a second burner arrangement 28 for thecombustion of a fuel/air mixture in the second combustion zone 24. Thesecond burner arrangement 28 comprises a premixing passage 29 whichopens into the second combustion zone 24 and which serves for theprovision of a fuel/air mixture, wherein an air supply 32, which isencompassed by the second burner arrangement 28, and a fuel supply 33open into the premixing passage 29, wherein the air supply 32 is ofstepped form such that the outlet openings 34, which open into thepremixing passage 29, of the stepped air supply 32 can be assigneddifferent delay times.

The second burner arrangement 28 is thus arranged in the region of asecond axial stage. The second burner arrangement 28 comprises a fueldistributor ring 36 arranged around the outside of the combustionchamber housing 21 and comprises multiple premixing passages 29, whereinthe premixing passages 29 open at one end 37 thereof into the secondcombustion zone 24 in the combustion chamber housing 21 and correspondin each case to a fuel supply 33 that branches off from the fueldistributor ring 36, wherein outlet openings 34 of a stepped air supply32 are arranged so as to be distributed along at least one of thepremixing passages 29.

In one advantageous refinement of the illustrated exemplary embodimentof the invention, each of the premixing passages 29 of the second burnerarrangement 28 may have a stepped air supply 32.

The fuel injected through the fuel supply 33 into the premixing passage29 mixes with the air entering the premixing passage 29 through theoutlet openings 34, such that a fuel/air mixture flows along thepremixing passage in the flow direction 39. An air volume exiting anoutlet opening 34 will mix with the fuel and, here, proceeding from theposition of the outlet opening 34, will require a time period in orderto pass into the combustion zone 24. Said time period is referred to asdelay time and is defined as the time required for a fluid elemententering the premixing passage to pass to the combustion zone. Theoutlet openings 34 arranged along the premixing passage 29 correspond,owing to their differing arrangement in the premixing passage 29, todifferent delay times. Each of the outlet openings 34 in the premixingpassage 29 can thus be assigned different delay times.

FIG. 3 shows a detail view of the combustion chamber according to theinvention illustrated in FIG. 2, according to an exemplary embodiment,in the region of the second burner arrangement of a second axial stage.The illustration shows a section of the combustion chamber housing 21which surrounds a first combustion zone 23 (partially illustrated) and asecond combustion zone 24 (partially illustrated) that adjoins saidfirst combustion zone downstream, wherein a premixing passage 29 whichis encompassed by the second burner arrangement and which serves for theprovision of a fuel/air mixture opens into the second combustion zone24. Into the premixing passage 29 which is of hose-like form there opensa fuel supply 33, which serves for the injection of fuel 35 into thepremixing passage 29, and an air supply 32 which is of stepped form. Theair supply 32 which is of stepped form comprises outlet openings 34 a,34 b, 34 c which open into the premixing passage 29 and which serve forthe supply of air 40, wherein the outlet openings 34 a, 34 b, 34 c canbe assigned different delay times τ₁, τ₂, τ₃. For example, an air volumeexiting the outlet opening 34 a will mix with the fuel 35 which has beeninjected through the fuel supply 33 and which is flowing past, and here,proceeding from the position of the outlet opening 34 a, will require atime period τ₁ to pass into the second combustion zone 24. For thedamping or suppression of a combustion chamber pressure fluctuation offrequency f, the position of the outlet openings 34 a, 34 b and 34 c mayadvantageously be selected such that τ₁−τ₃>1/f. The density fluctuationsof the air caused by the combustion chamber pressure fluctuation offrequency f in the outlet openings can, owing to the different delaytimes τ₁, τ₂, τ₃, be superposed during the ignition of the fuel/airmixture in the second combustion zone 24 such that said densityfluctuations substantially cancel one another out. The arrangement ofthe outlet openings 34 a, 34 b, 34 c along the premixing passage 29 maybe selected correspondingly for this purpose. The combustion chamberpressure fluctuation of frequency f may be a combustion chamber pressurefluctuation that can be predominantly excited owing to the configurationof the combustion chamber. This may also be referred to as predominantcombustion chamber pressure fluctuation. One refinement of theillustrated exemplary embodiment may also provide that the fuel supply33 is likewise of stepped form (not illustrated here).

1. A combustion chamber for a gas turbine comprising: at least onecombustion zone and at least one burner arrangement configured forcombustion of a fuel/air mixture in the combustion zone, the burnerarrangement comprising at least one premixing passage which opens intothe combustion zone and which provides a fuel/air mixture, at least onefuel supply which opens into the premixing passage, and an air supplywhich is of stepped form such that it comprises a plurality of outletopenings, each outlet opening opens into the premixing passage and isconfigured to provide air flowing through the premixing passage to thecombustion zone with a respective different delay time than air providedby the other outlet openings of the stepped air supply, wherein thedelay time is defined as the time required for a fluid element enteringthe premixing passage to pass to the combustion zone, wherein, for aminimum delay time τ_(min) and a maximum delay time τ_(max) of thestepped air supply with regard to a combustion chamber pressurefluctuation having a frequency f, which fluctuation is to be suppressed,the following applies: τ_(max)−τ_(min)>1/f, and the outlet openings ofthe stepped air supply, which open into the premixing passage arearranged such that the density fluctuations, caused by at least onepredominant combustion chamber pressure fluctuation of frequency f′, inthe fluid supplied through the outlet openings are superposed on oneanother in the premixing passage owing to the different delay timesassigned to the outlet openings, in such a way that the densityfluctuations substantially cancel one another out.
 2. The combustionchamber as claimed in claim 1, further comprising, the fuel supply whichopens into the premixing passage which is configured to be charged withgaseous fuel also is of stepped form.
 3. The combustion chamber asclaimed in claim 1, further comprising: the at least one combustion zonecomprises a first combustion zone followed downstream by a secondcombustion zone; the burner arrangement is arranged in the region of asecond axial stage of the combustion zone and includes at least onepremixing passage that opens into the second combustion zone (24), and asecond burner arrangement in the first combustion zone.
 4. Thecombustion chamber as claimed in claim 3, further comprising: the burnerarrangement comprises a fuel distributor ring arranged around an outsideof a combustion chamber housing around the combustion zone and theburner arrangement comprises multiple premixing passages, each beingopen at one end thereof into the second combustion zone in thecombustion chamber housing and each corresponding to at least one fuelsupply that branches off from the fuel distributor ring into thepremixing passage, wherein a plurality of the outlet openings of astepped air supply are distributed along at least one of the premixingpassages.
 5. A gas turbine comprising at least one of the combustionchambers, as claimed in claim
 1. 6. (canceled)
 7. The combustion chamberas claimed in claim 1, further comprising the outlet openings beinglocated distributed along the premixing passage, thereby to cause theminimum and maximum delay times by the location of the openings.